#include<stdio.h>
int main(void)
{
    double sum = 0;
    double t = 1,N;
    double j=1,k=1;

    scanf("%lf",&N);

    for(j=1,k=1;j<=N;j++){
        sum += t*(j/(double)k);
        k += 2;
        t = -t;
    }
    printf("%.3lf",sum);

    return 0;


    

}